1. Field of the Invention
This invention relates in general to a lens. More specifically, the present invention relates to an optical lens, a design method for the optical lens and a lens system using the optical lens.
2. Description of Related Art
In modern information society, a variety of optical systems, such as telescopes, cameras, microscopes and optical projection systems, is widely used in our everyday life. Lens in the aforementioned optical systems usually determines the image quality, and therefore, the conventional lens structure is further described for understanding function of lens.
FIG. 1 shows a cross-sectional view of a conventional lens. In FIG. 1, the lens 100 comprises a barrel 110, a first lens 120, a baffle 130, a second lens 140, a fixed plate 150, a filter 160, a sensor covering plate 170 and a charge coupled device (CCD) sensor 180. The barrel 110 has a light incident opening 110a and a receiving space 110b, and the light incident opening 110 is successive to the receiving space 110b. The first lens 120, the baffle 130, the second lens 140 and the fixed plate 150 are sequentially arranged within the receiving space 110b. The light incident opening 110a exposes a portion of the first lens 120 and a light outgoing opening 150a is formed on the fixed plate 150 to expose a portion of the second lens 140. The CCD sensor 180 is disposed at a light path behind the fixed plate 150. The sensor covering plate 170 is used to cover the CCD sensor 180 and is located on a light path between the fixed plate 150 and the CCD sensor 180. The filter 160 is disposed on a light path between the fixed plate 150 and the CCD sensor 180.
It should be noticed that a key step of making the conventional lens 100 is the alignment accuracy between the first lens 120 and the second lens 140. In an idea condition, the optical axis of the first lens 120 and the optical axis of the second lens 140 should be aligned. However, due to an assembling error, the optical axis of the first lens 120 and the optical axis of the second lens 140 will be misaligned. An eccentric shifting extent between the optical axis of the first lens 120 and the optical axis of the second lens 140 will affect the optical property of the lens 100. Referring to an enlarged portion shown in FIG. 1, in the conventional lens 100, the first lens 120 and the second lens 140 are positioned to align each other by arranging the first lens 120 and the second lens 140 against the inner wall of the barrel 110. Therefore, the processing accuracy of the inner wall of the barrel 110 will affect the alignment accuracy of the first lens 120 and the second lens 140. Currently, the barrel 110 is processed and worked by computer numerical control lathe (CNC lathe) or computer numerical control boring machine (CNC boring machine). The processing accuracy of the inner wall of the barrel 110 is only up to about 10 microns. Therefore, an alignment error between the first lens 120 and the second lens 140 is at least 5 microns or more. The conventional lens 100 using the barrel positioning method cannot be applied to high accuracy optical instruments. The optical property of the conventional lens 100 is further described according to an optical simulation analysis.
FIG. 2 is a diagram illustrating an optical simulation analysis for the conventional lens. A light ray 190 passes through in turns the light incident opening 110a of the barrel 110, the first lens 120, an opening of the baffle 130, the second lens 140, the light outgoing opening 150a of the fixed plate 150, the filter 160 and the sensor covering plate 170, and then is incident to the CCD sensor 180. A portion of the light ray 190 received by the CCD sensor 180 becomes an image light source 190a, and a portion of the light ray 190 becomes useless light 190b. The useless light will affect the image quality. The useless light 190b is mainly formed by that a portion of the light ray 190 is reflected by the filter 160 or the sensor covering plate 170 and then the reflected light is further reflected by fixed plate 150 or an interface (the baffle plate 130) between the first lens 120 and the second lens 140. Although the baffle plate 130 between the first lens 120 and the second lens 140 is made of black and low reflectivity material and used to absorb the useless light 190b, but the improvement by using the baffle plate 130 is not much.